Telegraph repeater



DIJCHARGED f L. B. HAIGH TELEGRAPH REPEATER Filed Dec. 4, 1946 RECEIVED M SIGNALS Sept. 12, 1950 Rbmmsmrrso SIGNALS INVENTOR LESLIE B. HA/GH ATTORNEY Patented Sept. 12, 1950 TELEGRAPH REPEATER Leslie Baines Haigh, London, England, assignor f to International Standard Electric Corporation,"

- New York, N. Y.

Application December 4, 1946, SerialNo. "114,691 i In Great Britain October 11, 1940 Section 1, Public 'Law 690, August 8, 1946 Patent expires October 11, 1960 Claims. coins-'70) 'This invention relates to telegraph repeaters and its main object is to reduce or remove a form of distortion which often affects the first impulse of a train of impulses re-transmitted by. a telegraph repeater.

According to the invention, a telegraph repeater for'the reception of trains of telegraph signals and for the re-transmission of said signals to a, line in the form of current impulses of two kinds, is characterised in this,- that in response to the reception of each train oftelegraph signals said repeater is arranged to precede the re-transmission of the first signal of the re-transmitted train by the transmission of a current impulse of the other kind.

Also according to the invention, a telegraph repeater for the reception of trains of telegraph signals and for the re-tr'ansmission of said signals to a line in the form of current impulses which are alternately in opposite directions of current flow, is characterised in this, that in response to the reception of each train of telegraph signals said repeater is arranged to precede the re-transmission of the first impulse of the re-transmitted train by the transmission of a current impulse in the opposite direction.

Also according to the invention, a telegraph re peater arranged to transmit marking and spacing' impulses over a line as substantially equal but opposite currents includes means responsive to a spacing signal forming the first signal of a train to transmit a marking impulse over the line and immediately thereafter to transmit a spacing impulse over the line.

-'I-he invention is particularly applicable to the form of telegraph repeater used for repeating trains of impulses transmitted by teleprinters in which each train of impulses represents a character and consists of a start impulse, five code impulses, and a stop impulse. In the commonly used teleprinter code, the start impulse of train is always a spacing impulse and the stop impulse is always a marking impulse.

In the system of alternate two-way transmission over a single-wire line commonly known as the switched simplex system, the line is nominally subjected at both ends to the same potential when no signals are passing in either direction. A character is transmitted by connecting to one end of the line, potentials alternately positive and negative with respect to the potential at the other end. The start signal, that is, the beginning of the start impulse, is a change at the one end from zero to spacing potential with respect to the potential at the other end, whereas the succeeding code. signals are full reversals- 0f It is foundin practice, especially'on potential. lines havingahigh time constant,that the impulse-receiving relay at the distant end responds more quickly to the start signal than to s'ucseeding signals with the result that the start im-- pulse is distorted by the relay- In order to 'over" come this form of distortion, the repeater circuit is modified according to the invention so as to precede the re-transmitted start signal-by a mark impulse of short duration. I i

An embodiment of the invention will now be described by way of example, reference. being made tothe accompanying drawin comprising Figs. 1 and 2.

Fig. .1 is axcircuitdiagramnof a telegraph ire-P peater according to the invention;

Fig; 2 is an explanatory. timingldiagram' the circuit of Fig. 1. v

,Fig. 1, shows a telegraph El of a telegraph relay or machine (not: shown) The signals received from El, and also those recept thefirst, as will be explained), an'dthose re-transmitted are also double current signals; In the embodiment being described, both ends of t 11ne L are provided with a telegraph repeater,

according to Fig. 1.

When no signals are passing in either direction,

armature El is standing on its marking contact M as shown, and current thereover from positive) battery through polarised relays SSand .T keeps: these relays intheir marking positions. Line L is connected over Tl. marking, Al back, polarised, relay R and resistance Q5, to ground; and armaa.

ture RI is standing on -its marking contact M (although-relay R is-nominally receiving no cur-.1. rent from line L) and is transmitting to Wire- P a steady marking potential.

When signals are-received by relay Rirom line L they are re-transmitted by El directly to wire P and none of the other relays is afiected. Con-1. denser K3 shunting partof resistance Q5 quickensthe response, and therefore improves the per-' formance, of. R. At the end of transmission, Rl'

returns to its marking contact M and then the marking potential atthe distant, endof line, L is:

repeater adaptedtoi re-transmit, toaisingleiwire line L, :teleprinter' signalsv received from the armature and contacts:

replaced by ground potential, so that R is deprived of current except for that which may be due to a difference in ground potential between the two ends of the line. BI is, however, sidestable and remains Standing on its marking contact M.

When signals comprising a teleprinter character are received from El for re-transmission to line L, the first signal is a spacing signal and El reverses to its spacing contact S. El closes a circuit for the quick operating relay A: negative battery, El spacing, Q3, Bl back, A, Q4, positive battery. A operates and disconnects R from line L. A also connects positive (marking) potential over Al front and TI marking to L, thus transmitting a preparatory marking signal to line L. El also reverses the direction of current flow through SS, the upper winding of T and resistance Ql and causes a discharge to flow in a tuned circuit comprising the lower winding of T, condenser KI and resistance Q2. Armature SSl reverses to its spacing contact S. The connections of the windings of T are, however, such that the eflfect on .this relay of the discharge through its lower winding opposes that of the current in the upper winding, and armature Tl remains standing momentarily on its marking contact M. Afterv an interval, the efiect of the current in the upper winding of T is dominant and TI reverses to its spacing contact S, disconnecting positive potential from line L and connecting negative (spacing) potential instead, thus transmitting a spacing signal to the line correspondingto the spacing signal received from El. The circuit constants are so chosen that A operates a short time, for example 5 milliseconds, before Tl reverses.

.Thus, the first signal received from El is retransmitted with a certain delay by TI, but is preceded by a short preparatory marking impulse, A

so that at the instant of re-transmission of the signal line L is subjected to a change of potential from positive to negative.

When a second signal, that is, a marking signal, is received from El, the direction of current flow in SS and the upper winding of T is reversed once more and a' discharge again occurs in the lower winding of T. Tl therefore reverses to its marking contact M after a delay which is' similar to the. above-mentioned delay, since the circuit including T and SS is symmetrical and the positive and negative potentials at El are supposed similar. The second signal received from El is thereby re -transmitted by Tl, line L being subjected to a change-of potential from negative to positive.

When SSI closes its spacing contact S as a consequence of the first signal received from El, as described, current flows in the upper Winding of relay B and, in addition, condenser K2 discharges through the lower winding of this relay. The connections of the windings of B are such that the discharge in the lower winding aids the current in the upper winding and B accordingly operates rapidly. At Bl, A is disconnected from negative potential over El and is connected instead to negative potential through relay C. C may have a non inductive winding connected in parallel with" its inductive winding i to prevent any tendencybf Atoreleas eat this stage. C operates and at Cl-short -circuits R; and- Q5, for a purpose to be: described? Resistance" Q3 serves to decouple the circuit, including AL BI and C,' fromthe cir-- cuit including T', SS'and El. The circuit'con-' s'tantsare so" chosenthat l B operates and disconnects A from El before the latter, under the most unfavourable conditions expected, can reverse again to its marking contact.

Subsequent signals received from El are 5 similarl retransmitted by TI, line L being subjected each time to a full reversal of potential. Every time El moves to its marking contact, SSl opens its spacing contact S. Condenser K2 then discharges through both windings of B in series. Although the effects of these windings are now in opposition, the upper winding is dominant and the discharge current is suflicient to hold B operated during any marking impulse occurring in the transmission of a character in the transmission of a character in the teleprinter code. Upon receipt of the marking signal ending each character, El moves to its marking contact M, Tl retransmits the signal to line L and SSl opens the circuit of B. If and when the pause after the reception of the signals comprising a character is long enough, B releases, disconnecting A from negative potential through C and reconnecting it through Q3 to El, now standing on its marking contact M. A accordingly releases and line L, which at the moment is charged to a certain potential, is connected over Tl marking and Al back to ground at Cl front, and discharges. B also opens the circuit of C which is, however, slow-releasing and remains operated long enough to ensure the discharge of line L. When Cl opens, line L is again extended through R and Q5 to ground and the circuit is now ready to receive signals from either direction.

Fig. shows diagrammatically the tim rela- 3 tons between the signals received from Bi and those transmitted to the line L, for the lettershiit" combination, taken by way of example, which combination consists in the teleprinter code 01 a single spacing impulse of 20 milliseconds nominal. duration. The thick horizontal lines represent the response times of the designated relays, e. ll+' represents the operating time of relay A, A represents the release time of relay A, T represents the time taken by relay to respond to a spacing signal, and T represents the time taken by relay T to respond to a marking signal. At a time represented to the left of line a the repeater circuit is receiving a steady marking signal from El and no signal is being transmitted to line L. At a, a spacing signal is received from El. At b, A operates and a marking signal is transmitted to line L. At 0, T responds to the spacing signal received from 12?, and TI re-transmits a spacing signal to the line. At d, nominally 20 milliseconds after a, a marking signal is received from El. In the meanime, SSl has reversed, B has operated and C is energized (it may have operated). At e, nominally 20 milliseconds after 0, T responds again and TI re-transmits a marking signal to the line. in the meantime, 55 has reversed again and, since no further spacing signal is received, B is .ed slowly. At f, B and A have both king potential is disconnected from L and the energy stored therein begins to At 0, C releases and R is reconnected It will be'apprcciated, therefore, that, whereas in th system commonly known as the switched the start signal is a change from ng potential, the start signal re- .ittcd by the telegraph repeater according to tneinvcntion is a change from marking potential to spacing potential, that. is, a signal ofsubstantially the same quality as those beginning the 3'! a? succeeding code impulses, and that this signal has been preceded by a preparatory marking signal.

When the preparatory marking signal reaches the other end of line L, the armature RI of the impulse-receiving relay R in the repeater thereat is already standing on its marking contact M, as described. Relay R, therefore, does not respond to this signal. Relay R, however, responds to the succeeding start signal and code signals. Since the start and code signals are of substantially the same quality, relay R responds thereto substantially without introducing distortion.

What is claimed is:

1. A telegraph repeater for the reception of trains of incoming telegraph signals of two different polarities and for retransmission of similar signals to an outgoing line, means connected to respond selectively in synchronism with the incoming Signals and their respective polarities to apply similar signals to said outgoing line, means responsive solely to the initial impulse of an incoming train to delay the action of said relay for a predetermined short time interval, and other means also solely responsive to said initial impulse to apply to said outgoing line during said interval an impulse having a polarity which is opposite to that of said initial impulse.

2. A telegraph repeater for the reception of trains of incoming telegraph signals of two different polarities and for retransmission of similar signals to an outgoing line, a first relay connected to respond selectively in synchronism with the incoming signals and their respective polarities to apply similar signals to said outgoing line, means associated with said first relay to delay its response for a predetermined time interval solely after the receipt of an initial incoming impulse, and a second relay also solely responsive to said initial impulse to apply to said outgoing line during said interval an impulse having a polarity which is opposite to that of said initial impulse.

3. A telegraph repeater according to claim 2, in which a slow-to-release relay is also provided which is operated solely in response to said initial 4 impulse, said slow-to-release relay when operated breaking the operating circuit of said second relay.

4. A telegraph repeater for the reception of trains of incoming telegraph mark and space signals of equal but opposite polarity currents and for retransmitting similar opposite polarity mark and space signals to an outgoing line, relay means solely responsive to a spacing signal which forms the first signal unit of an incoming train to transmit to said outgoing line a momentary marking signal for a predetermined time interval, and other relay means effective after said interval and selectively responsive to an incoming train to apply a similar train to said outgoing line.

5. A telegraph repeater for the reception of trains of incoming telegraph mark and space signals of different polarities and for retransmission of similar mark and space signals to an outgoing line, a pair of polarized relays to which the incoming signals are simultaneously applied, one of said relays having means to delay its response solely to the initial impulse of an incoming train, a first fast-acting relay controlled by the said second polarized relay, another fast-acting relay controlled solely by the initial impulse on an incoming train, a slow-to-release relay controlled by said first-mentioned fast-acting relay and operating substantially simultaneously therewith, and means controlled by the second-mentioned fastacting relay to apply to said outgoing line solely in response to the initial impulse of an incoming train, an impulse of a polarity which is opposite to that of said initial impulse.

LESLIE BAINES HAIGH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,146,234 Bruce July 13, 1915 1,386,679 Bell Aug. 9, 1921 2,230,681 Frischknecht Feb. 4, 1941 2,415,420 Dahlbom Feb. 11, 1947 

